In a conventional optical signal regenerator, especially in a conventional optical signal regenerator to regenerate high-speed optical pulse signals as fast as 40 Gbit/s in an intact optical state, an optical clock pulse train synchronizing with an input optical signal pulse train is gated by the input optical signal pulse train. Owing to this operation, even if a pulse waveform of the input optical signal is distorted, each pulse waveform of output optical signals becomes almost identical to that of the optical clock pulse train.
It is difficult to obtain a high-speed optical gate element. It is also difficult to stably generate a high-speed optical clock not only for technical aspects but also in terms of production costs. It is possible to generate a high-speed optical clock by multiplexing low-speed optical clocks in the time domain. However, a conventional optical pulse multiplexer is unable to gain sufficient pulse extinction ratios and it is yet unsatisfactory in respect of stability, quality, and costs.
Furthermore, in a high-speed optical pulse signal, to orthogonalize polarization directions of adjacent optical pulses is considered effective for suppressing interference between the adjacent pulses and also preferable for transmission characteristics. In a conventional configuration that utilizes an optical gate, it is necessary to modulate polarization of gate output light so that polarization directions of adjacent optical pulses orthogonalize at the gate output. However, it is difficult to obtain such a polarization modulating element that operates at high-speed and has such functions described above.